Electrochemical fluorination of polymethylene sulfones to produce perfluoroalkylsulfonyl fluorides



United States Patent tion of Michigan No Drawing. Filed Nov. 22, 1965, Ser. No. 509,210

2 Claims U.S. Cl. 204-59 Int. Cl. Bollr 3/00 This application relates to a new process for the production of perfluoroalkylsulfonyl fluorides, which are valuable intermediates for the preparation of agents for rendering fabrics oleophobic, and which are useful as surfactants in their own right.

U.S. Patent 2,519,983, issued to Simons, discloses the electrochemical fluorination of organic materials with anhydrous hydrofluoric acid. US. Patent 2,732,398, issued to Brice and Trott, discloses the use of the process of Simons to convert hydrocarbon sulfonyl halides into perfluoroalkylsulfonyl fluorides.

This invention relates to the process of electrolyzing a current-conducting mixture of a composition consisting essentially of a liquid solution of 0113 CH3 CH3 CnHrsC CH2CH-CHCH2? Oz.

and

(C2H5)2C HM S 2.

They are known compositions which are made by the reaction of the appropriate alpha-omega-diolefin (e.g. butadiene) with S0 The major advantage of the process of this invention is its relatively high yield of product, which renders it commercially desirable. The process is also unique in that the electrochemical fluorination process has never before been found to cause ring cleavage at a carbonsulfur linkage to form a perfluoroalkylsulfonyl fluoride.

The preferred reactant is tetramethylene sulfone because of its ready availability.

Details concerning the types of electrolytic cells and operating procedures which are useable in this invention are available in the Simons patent and the Brice, et al. patent, both of which are cited above.

The process of this invention is generally performed at a low temperature, usually under C., in order to 3,423,299 Patented Jan. 21, 1969 easily maintain the hydrogen fluoride in the liquid form without the use of pressure. The alkylene sulfone ingredients are generally quite soluble in liquid hydrogen fluoride.

The conductivity of the alkylene sulfone-hydrogen fluoride solution is usually adequate to permit electrolysis at a sufliciently low voltage to prevent the evolution of elemental fluorine, which begins to form when about 10 to 12 volts are applied to a cell anode. However, small amounts of conductivity additives such as sodium or potassium fluoride can be added, if desired. When a nickel anode is used, voltages of from 4 to 8 volts generally give the best results.

It is preferred for an excess of hydrogen fluoride to be present so that there is more than enough fluorine available for reaction with the sulfone, but the proportion of the two reactants to each other is not critical to the operability of this invention. The yield of perfluoroalkylsulfonyl fluoride will, however, be greatly increased when a substantial excess of hydrogen fluoride is used,

The term essentially anhydrous is intended to imply that trace of water can be present in the hydrogen fluoride, but that the water content should not be more than about 2 percent in order to avoid undesirable side reactions and the increased corrosiveness of aqueous HF.

It is preferred to operate the cell on one polarity with direct current although alternating current is operative.

Several hours or days of operation are generally required in order to maximize the yield of the process of this application.

The electrochemical cell itself is best made of any nonreactive metal, e.g. nickel, Monel, gold plate, or molybdenum. The cell can also be made of graphite or fluorocarbon plastics, if desired.

The cathodes and anodes can be made of any conductive material which is not corroded by anhydrous HF, e.g., nickel, Monel, carbon, silicon carbide, etc.

The following examples are illustrative only and should not be construed as limiting the invention which is properly delineated in the appended claims.

EXAMPLE 1 An electrochemical cell was prepared and fitted with a nickel anode and cathode and with a condenser designed to trap and return all volatiles condensing at l5 C. or above and evolving from the cell. The top of the condenser was vented out of doors.

The cell was cooled to l0 C., and anhydrous HF vapor was added until about 3500 ml. of liquid HF were present in the cell. To this was added 1242.5 g. of tetramethylene sulfone, and the cell was operated for 5 days at about 0 C. with a direct current of about amperes and 5.5 volts.

Following this, 1443 grams of crude cell product were drained from the cell. Analysis by gas-liquid chromatography indicated that about 94 percent by weight of the crude product was CF CF CF CF SO F, which amounts to over a 40 percent yield, based on the tetramethylene sulfone reactant.

EXAMPLE 2 When an electrochemical cell, fitted with a graphite anode and cathode and the same condenser as in Example l is filled with 1 kg. of octamethylene sulfone and 2 kg. of liquid HF, electrolysis for several days at 10 C. at a voltage of 7 volts produces a liberal yield of nperfluorooctylsulfonyl fluoride.

EXAMPLE 3 When the experiment of Example 1 is repeated with the substitution of hexamethylene sulfone for the tetra- 3 methylene sulfone ingredient, a high yield of n-perfluorohexylsulfonyl fluoride is recovered.

EXAMPLE 4 CHzCHz in 200 or 300 ml. of liquid, anhydrous hydrogen fluoride.

Electrolysis was initiated at 10 C., and an average current of 85 amperes and 5.5 volts was maintained for 48 hours with an average temperature of C. At the end of the period, the current began to decrease. When it had fallen to 15 amperes, the electrolysis was discontinued, and 532.4 g. of a water-white crude cell product was drained from the bottom of the cell.

Analysis showed the cell product to contain 28.6 mole percent of OFJCFgSiFCFISOZF CF; and 28.0 mole percent of CFzOFCFzCFzSOzF EXAMPLE When the experiment of Example 4 is repeated with the substitution of for the sulfone ingredient used above, a liberal yield of C4F9CF2CF2CF2CF2SO2F and CqFs is formed.

That which is claimed is: 1. The process of electrolyzing a current-conducting mixture of a composition consisting essentially of a liquid solution of References Cited UNITED STATES PATENTS 8/1950 Simons 1/1956 Brice et a1.

HOWARD S. WILLIAMS, Primary Examiner. 

1. THE PROCESS OF ELECTROLYZING A CURRENT-CONDUCTING MIXTURE OF A COMPOSITION CONSISTING ESSENTIALLY OF A LIQUID SOLUTION OF 